I guess it depends on the call for me. Wrecks and such that im not in a pack, I wear it over my gear. If Im in a pack it goes in my radio pocket. My is a boston leather set-up that came from thefirestore.com i think, my wife got it for me for chrismas i think.
When I first saw someone with these straps I thought they (the straps) were stupid. I quickly changed my mind once I decided to start wearing one...a decision based on functionality, not looks. I really believe the use of lapel mics help with improved communication...and the radio strap helps the lapel mic stay put (especially from becoming unclipped from your shirt).
I purchased my personalized strap from a brother in Florida (www.hookandladderleather.com). I wear it over my gear (coat) and under it during fire calls when I wear an SCBA (alarm investigations, gas leaks, fires). When I get dispatched to a fire call I put my hood and pants on, then my radio strap, then my coat. I unclip the lapel mic from the strap and run the speaker/mic out of the neck hole...then it is cliped to my coat collar next to my ear. I have adjusted the length of the strap so that my radio rests on my hip just below where I wear the "waist belt" on my SCBA. I have never had any issues with this setup...but I have had some naysayers mention these arguements for not using a strap:
"what if you have to change the channel on your radio?"
I can usually make the change by just lifting up my coat / adjust my SCBA...a few times I have had to unbuckle the waist belt before I can get access to the radio. You should never have to change your radio channel in an IDLH environment...I don't know how anyone would be able to see the channel in most fires anyway.
"The radio gets in the way"
If you purchase the anti-sway strap AND use it then you shouldn't have any problems with your radio getting in the way.
Radio straps are a matter of personal preference...and mine is to wear one.
Hope this helps.
Of course... another great supplier of custom leather firefighter equipment (radio harnesses, straps and axe belts), along with a fellow brother from Washington/Oregon can be found at www.TraditionalFireLeather.com
I have no doubt that you will enjoy and come to depend upon the products found there.